introduced by Donoho and Tanner (with different notation). For fixed \(\delta \in (1/2,1)\) , the function \(G_\delta \)  defined by \(G_\delta (x):= G(\delta ,x)\)  has a unique zero in \([0,1]\)  (see, e.g., Lemma 6 in [1]}), which is denoted by \(\rho _S(\delta )\) .
